Magnetic head with printed circuit coil

ABSTRACT

An array of read-write heads for a magnetic storage means, such as a disk or drum, is disclosed. Each head is comprised of a flux carrying means, such as a gapped ferrite loop and a fluxproducing means, such as a pair of coils inductively coupled to the loop. The coils, together with a portion of the associated addressing circuitry, are supported by a substrate. The halves of the ferrite loops that lie on opposite sides of the substrate are formed as separate ferrite parts. The halves of the ferrite loops are disposed on opposite sides of the coil assembly so that the halves of the loops mate through holes in the substrate and form the gapped ferrite loops. In one embodiment, the halves of the ferrite loops are partially formed on the faces of ferrite blocks which support the loop halves during fabrication. After the halves are assembled on opposite sides of the substrate, the excess material of the ferrite assemblies is cut away to leave the discrete ferrite loops and the associated coils embedded within a solid structure which also appropriately isolates the parts electrically and magnetically. In another embodiment, the halves of the ferrite loops are formed individually and supported by a ceramic housing during mating with the coil assembly and the other halves of the loops. The substrate can be an insulator, such as glass, in which case the coil circuitry can be a photographically patterned metal film and the addressing diodes discrete semiconductor devices. Or the substrate can be a semiconductor, in which case either the coils or the addressing diodes, or both, may be diffused in the sheet of semiconductor material. Or the substrate may be a selectably reducible material such as YIG or Ti02 in which conductive paths can be selectively formed in the substrate by a scanned energy beam. Or the substrate may be the face of a subassembly for holding either of the halves of the ferrite loops prior to final assembly, or coils may be formed on the faces of both subassemblies.

Richards, Harris and Hubbard United States Patent [151 3,648,264 Gruczelak et al. [4 Mar. 7, 1972 [57] ABSTRACT 1541 MAGNETIC HEAD WITH PRINTED CIRCUIT COIL [72] Inventors: Norman P. Gruculak, King of Prussia,

Pa.; .Ioe T. Plerce, Richardson, Tex. [73] Assignee: Texas Instruments Incorporated, Dallas,

Tex.

[22] Filed: Sept. 30, 1968 [21] Appl. No.: 763,751

[52] US. Cl. ..340/l74.l F, 29/603, 179/ 100.2 C

[51] Int.Cl ..Gllb 5/20,Gllb5/42 [58] Field of Search ..340/174.1F; 179/100.2 C; 346/74 MC [56] References Cited UNITED STATES PATENTS 2,917,589 12/1959 Kornei ..l79/ 100.2

3,240,881 3/1966 Oliver ..179/ 100.2

3,344,237 9/1967 Gregg... ..l79/l00.2

3,505,662 4/ l 970 l-libner' i 79/ 1 00.2

2,908,770 10/1959 Warren.... ..179/100.2

3,085,246 4/1963 Cowden... ..179/100.2

3,104,455 9/1963 Frost ..l79/l00 2 3,145,453 8/1964 Doinker et al. .....l79/100 2 3,323,116 5/1967 Solyst ..179/l00.2

3,353,261 11/1967 Bradford et al 179/1002 3,317,742 5/1967 Guerth ..340/174. 1

3,549,825 12/1970 Trirnble 179/ 100.2 C

Primary Examiner-Bernard Konick Assistant Examiner-Vincent P. Canney Attorney--Samuel M. Mims, Jr., James 0. Dixon, Andrew M.

Hassell, Harold Levine, Rene E. Grossman li/Iel vi n Sharp and An array of read-write heads for a magnetic storage means, such as a disk or drum, is disclosed. Each head is comprised of a flux carrying means, such as a gapped ferrite loop and a fluxproducing means, such as a pair of coils inductively coupled to the loop. The coils, together with a portion of the associated addressing circuitry, are supported by a substrate. The halves of the ferrite loops that lie on opposite sides of the substrate are formed as separate ferrite parts. The halves of the ferrite loops are disposed on opposite sides of the coil assembly so that the halves of the loops mate through holes in the substrate and form the gapped ferrite loops.

1n one embodiment, the halves of the ferrite loops are partially formed on the faces of ferrite blocks which support the loop halves during fabrication. After the halves are assembled on opposite sides of the substrate, the excess material of the ferrite assemblies is cut away to leave the discrete ferrite loops and the associated coils embedded within a solid structure which also appropriately isolates the parts electrically and magnetically.

In another embodiment, the halves of the ferrite loops are formed individually and supported by a ceramic housing during mating with the coil assembly and the other halves of the loops.

The substrate can be an insulator, such as glass, in which case the coil circuitry can be a photographically patterned metal film and the addressing diodes discrete semiconductor devices. Or the substrate can be a semiconductor, in which case either the coils or the addressing diodes, or both, may be diffused in the sheet of semiconductor material. Or the substrate may be a selectably reducible material such as G or Ti0 in which conductive paths can be selectively formed in the substrate by a scanned energy beam. Or the substrate may be the face of a subassembly for holding either of the halves of the ferrite loops prior to final assembly, or coils may be formed on the faces of both subassemblies.

1 Claims, 13 Drawing Figures PaIemed March 7, ID?2 4 Sheets-Sheet ADDRESS LINES ADDRESS DECODER 0 DATA BIT OUT ea 'ZOREAD INHIBIT WRITE COMMAND 0 DATA BIT INPUT DATA BIT DDT 88 0 READ INHIBIT Q WRITE COMMAND ODATA BIT INPUT Meme-d March 7, 1972 4 Sheets-Sheet :5

MAGNETIC HEAD WITI-I PRINTED CIRCUIT COIL This invention relates generally to magnetic data storage, and more particularly relates to arrays of magnetic read-write heads used in data processing to write on and read from magnetic disk and magnetic drum memories.

Magnetic disk and magnetic drum memories are used extensively in computers because of their reasonable cost and high access rates. Two basic types of read-write systems are used in connection with these memories. In one, a separate read-write head is provided for each data track. This has the advantage of reducing the maximum access time to one revolution of the disk or drum, but has the disadvantage of requiring a very large number of heads. The other type provides a single readwrite head for a number of tracks and moves the head by means of a digital or analog positioning mechanism. This system has a slower access time, which is basically the sum of the maximum head positioning time and the disk revolution time. Most large disk memories utilize a movable head system because the principle difference in cost between the two systems is the cost of the individual magnetic heads.

In order to achieve maximum storage, the fixed magnetic heads must be very small, thus making their manufacture relatively expensive. For example, it is necessary to have as many as 16 magnetic heads per linear inch, and even then two or more staggered rows are required to achieve maximum storage capacity. For optimum operation, the heads must be located very close to the recording medium. The arrays of heads are customarily supported about 100 microinches above the recording media by an air film upon which the array floats. The array and recording media must, therefore, be essentially optically flat over the width of the array and may have a length of about one inch.

The current procedure for fabricating these arrays involves grinding individual gapped ferrite loops, then winding very small wires around each leg of each loop to form a pair of coils. The head assemblies are then positioned in a holder machined from a nonmagnetic material and bonded in place, while keeping the many lead wires to the individual coils in the proper place. The face of the array is then ground and lapped, and finally the lead wires are connected to the appropriate addressing circuitry. Because of the very small size and individual handling required, the cost of this procedure is relatively high and has been a primary limiting factor in the use of a read-write systems having an individual pickup head for each track on the storage media.

This invention is concerned with a method for fabricating arrays of read-write heads which is sufficiently economical to make systems using a separate read-write head for each data track comparable in cost to the much slower indexing type system, and with the' resulting product.

The read-write head in accordance with this invention is comprised of a plurality of individual heads each formed by at least one coil supported by a substrate, and a magnetic loop inductively coupled to the coil. The magnetic loop is formed by upper and lower ferrite halves lying generally on opposite sides of the substrate. The lower ferrite half includes a nonmagnetic sensing gap. Additional, more specific aspects of the array are also claimed.

In accordance with the process of this invention, the coils for the array are formed on a common substrate and the gapped ferrite loop is then built around the substrate by joining two ferrite loop halves, one containing the sensing gap, through the respective coil on the substrate.

In accordance with one specific aspect of the invention, the upper and lower halves are formed in the appropriate relative positions in upper and lower subassemblies which are then mated on opposite sides of the coil substrate and the three parts bonded together by a potting material. The excess material of the subassemblies is then removed.

In accordance with another specific aspect of the invention, the array can be fabricated by positioning one set of individual ferrite halves in a nonmagnetic body, then successively positioning the substrate and the other ferrite halves in position and bonding the parts into a solid structure with a potting material.

The novel features believed characteristic of this invention are set forth in the appended claims. The invention itself, however, as well as other objects and advantages thereof, may best be understood by reference to the following detailed description of illustrative embodiments, when read in conjunction with the accompany drawings, wherein:

FIG. 1 is a bottom view of an array of read-write heads constructed in accordance with the present invention;

FIG. 2 is a sectional view taken generally on lines 2--2 of FIG. I, the right-hand portion of the drawing being shown in an intennediate stage of completion;

FIG. 3 is a sectional view taken generally on lines 3-4 of FIG. 2, the right-hand portion of the drawing being shown in an intermediate stage of completion;

FIG. 4 is an exploded isometric view of the components used to fabricate the device of FIG. 1;

FIG. 5 is a plan view of the top side of the coil assembly of the device of FIG. 1',

FIG. 6 is a plan view of a portion of the bottom side of the coil assembly of FIG. 4;

FIG. 7 is a schematic circuit diagram illustrating how the array of FIG. 1 may be utilized; and

FIG. 8-13 are simplified isometric views which illustrate the steps of another method for fabricating a read-write array in accordance with the present invention.

Referring now to the drawings, and in particular to FIG. I, an array of read-write heads fabricated in accordance with the present invention is indicated generally by the reference numeral 10. In the embodiment illustrated, 16 heads 11 are arrayed in two staggered rows, eight in each row, as can be seen in the bottom view of FIG. 1, although other numbers of heads may be utilized as desired.

The array 10 is shown in completed form in the left-hand portions of FIGS. 2 and 3 and at an intermediate stage of manufacture in the right-hand portions. Each read-write head I 1 is comprised of a discrete ferrite loop 12 which is generally U-shaped and has a base section and leg sections 12b and 12c the ends of which are spaced apart to provide a gap 14. A pair of coils 16b and are fonned around the legs 12b and 12c of the loop 12 by patterned metal layers deposited on both sides of a substrate 20. Addressing diodes 22b and 220 are connected to the coils 16b and 16c, respectively, as will presently be described. These components are encased in a suitable nonmagnetic and dielectric potting material such as commercially available glass filled epoxy which may be applied in several steps as will hereafter be described in greater detail. The lower face 28 of the array is optically flat and the leading edge 30 is beveled at a slight angle so that the device will float on a thin film of air as a magnetic storage disk is rotated at high speed in the direction of arrow 32 (see FIG. 2) under the lower face 28. Expanded contact pads 34 are provided along the edges of the substrate 20 which protrude from the body of potting material. The contact pads 34 are used to connect the array into the remainder of the read-write circuitry. Other details of the array 10 will become more evident as the process for fabricating the array is described in detail.

The process for fabricating the array 10 in accordance with this invention will now be described. A coil assembly, indicated generally by the reference numeral 40 in FIG. 4, is fabricated on a substrate 20, which may be either an insulator, such as glass, a high-resistivity semiconductor, such as silicon, a selectively reducible material such as YIG (yttrium iron garnet) or TiO (titanium dioxide), or other suitable material. The substrate is typically about eight mils thick and on the order of 1 inch square. The substrate is first thoroughly cleaned, then both sides coated with a thin film of metal by conventional evaporation, sputtering or other vacuum deposition technique. A conventional chromium-gold system may be used for this purpose. Both sides of the substrate are then protected with a photoresist mask while 16 pairs of holes 42b and 42s, arrayed in two staggered rows of eight pairs each, and sixteen feedthrough holes 44 are simultaneously etched through the metal layers and through the substrate from the opposite sides. The metal layers are then stripped from both sides of the substrate and new layers of the same metal reapplied to both sides of the substrate. During the latter deposition, the edges of the holes 42b, 42c and 44 are also coated with metal so that the metal layers on the opposite faces of the substrate are electrically interconnected. The metal layers on the top face are then patterned as illustrated in FIG. 5, and the bottom face is patterned as illustrated in the partial view of FIG. 6 using conventional photolithographic techniques.

As will be noted in FIG. 5, the coils 16b and 16c are disposed around the openings 42b and 42c, respectively, and extend outwardly and terminate as conductors 46b and 46c. A first bus 48b has branches which extend along the outside of the two rows of coil pairs. A second bus 48c extends from a contact pad at one edge of the substrate 20 and extends between the two rows of coil pairs. The plurality of contact pads 34 are disposed along the edges of the substrate. As will be noted in FIG. 6, the circuitry on the bottom of the substrate 20 includes the other halves of the coils 16b and 16c, which are in electrical contact with the portions of the coils on the top surface through the openings 42b and 42c, and conductors 52, which are electrically connected to the expanded contacts 34 on the top face through the apertures 44. A diode 54b connects each coil 16b to the bus 48b. The semiconductor diodes are bonded directly to the bus 48b, and are connected to conductor 46b by a ball-bonded jumper wire. Similarly, a diode 54c connects each coil 16c to the bus 48c.

The equivalent circuit is illustrated schematically in FIG. 7 where corresponding parts are designated by corresponding reference characters. The portion of the circuit included in the coil assembly 40 is indicated by the dotted outline 40 in FIG. 7. The circuit extending from contact pads 34 on the top surface through the apertures 44 to the conductor 52 on the bottom surface forms a center tap which is connected between the coils 16b and 16c, each of which is formed half on the bottom surface and half on the top surface as previously described. The circuit continues through diodes 54b and 540 to the common buses 48b and 48c, respectively. Operation of the circuit shown in FIG. 7 is hereafter described in greater detail.

An upper ferrite subassembly, indicated generally by the reference numeral 58 in FIGS. 2-4, is machined from a ferrite block so as to leave sixteen base portions 12a protruding from the lower face. Each of the base portions 12a includes a pair of stubs 60b and 60c which have a length approximately equal to the thickness of the coil assembly 40. A layer 61 of nonmagnetic and dielectric material, such as glass filled epoxy, covers the lower surface of the ferrite block. The layer 61 may be applied after the base portions 12a are formed by machining cross channels in the lower face of the ferrite body 58. Then both the layer 61 and the ferrite body can be simultaneously machined to leave stubs 60b and 60c.

A pair of identical ferrite parts 64b and a pair of identical ferrite parts 64c are then machined as illustrated in FIGS. 2-4. It will be noted that leg portions 12b extend upwardly from parts 64b and legs 12c extend upwardly from parts 64c. A part 64b is then paired with a part 64c, separated only by a thin layer of nonmagnetic material, to form a gap 14. The gap 14 is typically about 25,000 angstroms thick. The thin layer of nonmagnetic material may be used to bond the two ferrite parts 64b and 64c together, or the ferrite parts can be bonded together by a material at points other than the points where the gaps 14 are to be formed.

The upper ferrite subassembly 58 may then be laid on a flat surface with stubs 60b and 600 projecting upwardly. The face 62 of the layer 61 of dielectric material can then be coated with a suitable conventional dielectric and nonmagnetic bonding material, such as glass filled epoxy, and the coil assembly 40 inverted and placed such that the stubs 60b and 60c project through the respective apertures 42b and 42c. The bottom face of the coil assembly 40, which may conveniently be facing upwardly for this step, is then coated with the bonding material and the assembled pairs 64b and 64c positioned such that the ends of the legs 12b and abut against the ends of the stubs 60b and 60c, respectively, in the respective rows.

After the dielectric bonding material has hardened, the structure is substantially as illustrated in the right-hand sections of FIGS. 2 and 3 wherein the bonding material used to connect the upper ferrite subassembly 58 to the top face of the substrate is indicated by the reference numeral 66, and the bonding material used to connect the assembled pairs 64b and 640 to the bottom face of the substrate is indicated by the reference numeral 68. After the bonding material has hardened, the excess portion of the upper ferrite subassembly 58 is removed along dotted line 70, and the excess portions of parts 64b and 64c and the bonding material 68 are removed along dotted line 72 to form the lower face 28 which is then lapped and polished optically flat. The leading edge 30 is then beveled to complete the structure.

In accordance with another aspect of the invention, the substrate 20 of the coil assembly 40 may be a high-resistivity semiconductor material. In that case, the diodes 54b and 54c, and also the coils 16b and if desired, may be formed in the semiconductor substrate by a conventional double diffusion process, and then interconnected in the control circuit for the respective coils by appropriately patterning the metal layers. The substrate for the coil assembly may also be a selectively reducible material such as yttrium iron garnet (YIG) or titanium dioxide (TiO which may be reduced in selected areas from a nonconductive material to a conductive material by a scanned beam of energy such as an electron beam. Or the substrate upon which the coils are formed may be a flexible plastic material such as H-film which is polypyromellitimide plastic sold under the trademark Kapton by DuPont, or other suitable material. The use of a separate semiconductor substrate provides the advantage of utilizing a coil on both faces of the substrate, thus giving a maximum number of turns for a given line width, in a given area. If desired, the upper ferrite subassembly 58 may be used as the substrate, in which case the coils can be formed directly on the lower face of the subassembly 58. Conversely, the legs 12b and 120 can be incorporated into a lower substrate assembly and the coils formed on the upper surface of that assembly. Or, coils can be formed on the faces of both the upper and lower assemblies, and separated by a thin layer of insulation with electrical feedthrough, as required, after assembly. The stubs 60b and 60c which extend through the coils may project from either the upper ferrite subassembly 58 or from the leg portions 12b and 120 of the lower substrate assembly. The stubs 60b and 60c may also be formed by a patterned layer of magnetic material, such as a photoresist filled with ferrite powder. Also, the stubs 60b and 60c may be formed by chemical etching, sandblasting, or techniques other than machining.

A plurality of arrays 10 can be operated by the control circuitry illustrated in FIG. 7, where the portion of the circuitry on each coil assembly 40 is defined by the dotted line 40. An address decoder 80 operates one of the drivers 82 so as to supply current through the center tap 34-52 to forward bias the diodes 54b and 54c and enable one read-write head on each array in the system. The voltage induced in the coils 16b and 16c of the enabled head of a particular array can then be read through the diode switching matrix 84 and differential amplifier 86 which is selected by switching the logic control line 88 to a low potential. Similarly, any one of the heads enabled by current from a driver 82 can be used for writing by actuating the corresponding write amplifier 90. The circuitry for operating the arrays is of conventional design and does not constitute a part of this invention.

Another method for fabricating an array of read-write heads in accordance with the present invention is illustrated in FIGS. 8-13. A ferrite piece 210 is machined as illustrated in FIG. 8. The ferrite piece 210 has a base portion 210a, an upstanding flange portion 210b, and a very flat face 212 extending along one edge of the base portion. The edge 212 is then coated with a thin highly uniform layer of nonmagnetic material 214, such as glass. The nonmagnetic layer 214 is typically about l2,500 angstroms thick, and may be deposited using a conventional vacuum deposition process such as RF sputtering.

The piece 210 is then cut in half and the opposite halves mated as illustrated in FIG. 9 so that the nonmagnetic layers 214 are in abutting relationship. The two pieces 210 are then bonded together by a suitable nonmagnetic material 216 deposited in the trough formed between the flange portions 21%. The nonmagnetic material 216 may be a glass-filled epoxy.

Next, a slot is machined in the assembly illustrated in FIG. 9 to produce the assembly as illustrated in FIG. 10. It will be noted in FIG. 10 that the flange portions 21% have been substantially reduced in width to leave flanges 218 which protrude above a face 220 which extends across the nonmagnetic material 216. The upper faces 218a of the flanges 218 are preferably very flat and parallel to the face 220.

The assembly of FIG. 10 is then sliced along dotted line 222 to provide a final part 224 illustrated in FIG. 11 having upwardly projecting posts 225 with flat top surfaces 2180. The part 224 constitutes the half of a magnetic loop for a readwrite head that contains the nonmagnetic sensing gap, which is formed by the nonmagnetic layers 214. The other half of each magnetic loop is comprised merely of a small piece of ferrite material which is sized to bridge between the surfaces 218a of the loop half 224 and which may be comprised by slicing a thin sheet of ferrite material 226, as illustrated in FIG. 12, along dotted lines 228 to provide the upper loop halves 230.

The magnetic loops may then be assembled into an array of read-write heads as illustrated in the exploded isometric view of FIG. 13. The lower magnetic loop halves 224 may be placed into slots 232 in a ceramic housing 234 and may rest on a highly planar reference surface which also supports the hous ing 234. The housing 234 has a pair of flat surfaces 235 which ride on a thin film of air between the magnetic recording media and the array to support the array. A coil assembly 236, which may be very similar to the coil assembly 40 of FIG. 4, is then placed over the lower loop halves 224 with the posts 218 projecting through apertures 238. The upper magnetic loop halves 230 may then be placed in position on the upper surfaces 218a of the respective lower loop halves. The expanded metallized contacts 240 on the coil assembly 236 may then be connected to contact pads represented at 242 on the housing 234 using any suitable conventional technique, such as ball bonded jumper wires. The entire assembly may then be filled with a suitable nonmagnetic and dielectric liquid potting material to hold the various parts in place and provide a solid structure.

If desired, the procedure for assembling the array in FIG. 13 can be reversed. For example, the upper magnetic loop halves 230 can be placed in a suitable holder, the coil assembly 236 inverted and placed on the upper loop halves 230, the lower loop halves 224 then placed in position in the respective apertures 238 of the coil assembly, and finally a lower housing placed around the coil assembly 236 to form the side walls of a receptacle for receiving the liquid potting compound and the flying pads. The liquid potting compound would then be poured into the receptacle to provide a completely solid structure.

Although preferred embodiments of the invention have been described in detail, it is to be understood that various changes, substitutions, and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

What is claimed is:

1. An array of magnetic read-write heads comprising:

a. at least one semiconductor substrate, said substrate having contiguous regions of P and N conductivity type, said contiguous regions forming a plurality of semiconductor diodes;

b. a plurality of patterned electrically conductive regions positioned around apertures in said substrate and selectively connected to said semiconductor diodes; and

c. a plurality of magnetic flux carrying means positioned in said apertures such that said magnetic flux carrying means are magnetically coupled to said patterned electrically conductive regions, said flux carrying means including at least one region having lower magnetic permeability, thereby forming an array of magnetic read-write heads with each head having a flux-sensing area formed by said region of low magnetic permeability and an addressing network formed by said semiconductor diodes. 

1. An array of magnetic read-write heads comprising: a. at least one semiconductor substrate, said substrate having contiguous regions of P and N conductivity type, said contiguous regions forming a plurality of semiconductor diodes; b. a plurality of patterned electrically conductive regions positioned around apertures in said substrate and selectively connected to said semiconductor diodes; and c. a plurality of magnetic flux carrying means positioned in said apertures such that said magnetic flux carrying means are magnetically coupled to said patterned electrically conductive regions, said flux carrying means including at least one region having lower magnetic permeability, thereby forming an array of magnetic read-write heads with each head having a flux-sensing area formed by said region of low magnetic permeability and an addressing network formed by said semiconductor diodes. 